If you can frost a cake, you can learn to use a palette knife!
When I am painting outdoors, my favorite tool is my palette knife. It helps me to work quickly by simplifying shapes and not getting to fussy with tiny details which I can be tempted to do with brushes. I love the interesting marks and thick impasto that only a painting knife can give a painting. And an added bonus is clean-up is a snap with just wiping the knife off with a paper towel!